1. Field of the Invention
This invention relates generally to a semiconductor device, and more particularly to a transistor in which a diffusion length of minority carriers in an emitter region is larger than that of conventional transistors.
Such transistors were described in patent applications of Hajime Yagi and Tadaharu Tsuyuki, Ser. No. 427,647 and 427,648 filed Dec. 26, 1973, assigned to the same assignee as this application.
In one of the above patent applications, Ser. No. 427,648, the built-in-field located in the emitter region is specified. In the other patent application, Ser. No. 427,647, the re-injection source region and other special means formed adjacent the emitter region are specified.
2. Description of the Prior Art
The emitter region of the transistor is generally formed by heavy doping of impurity material into a semiconductor material, and the diffusion length of minority carriers therein is very small in comparison with a width of the emitter region.
Some of the prior arts show transistors having a lightly doped emitter region therein. For example, U.S. Pat. Nos. 2,822,310, 3,500,141, 3,591,430 and French Patent Publication No. 2,130,399.